Pull air out and push cold air in is the best option, if you only have 1 fan then, pull the hot air out, cold air will be pulled in from any unsealed paths.
I don't fully agree with this but it does depend on the size of your mining operation. I have 200 GPUs in a 1800 sqft warehouse and initially due to lack of air flow/moving air, the air temperature rose to almost 50C... and this was with two exhaust fans pulling air out.
Changing the setup to have one intake fan resolved the problem and air temperatures inside now a happy 30C.
Thats very interesting and maybe i am wrong on this occasion. I am not sure where the hot air would be going if you are only blowing colder air in